Reversi Online — Play Othello vs Computer

Play Reversi — the disc-flipping strategy game standardised as Othello — free in your browser, against the computer or with a friend in pass-and-play on one screen. The rules are faithful to the modern game: Black moves first from the standard diagonal centre setup, a move is only legal if it outflanks at least one straight line of enemy discs, every flanked disc flips to your colour, you pass when you have no legal move, and when neither side can move the player with the most discs wins.

The four computer levels are genuinely different opponents, not just timers. Easy plays random legal moves, Medium greedily grabs the most flips, Hard plays positionally using a weighted board map that prizes corners and punishes the poisonous squares beside them, and Expert runs a minimax search with alpha-beta pruning — looking four to six moves ahead and judging positions on board weights, mobility and corner control. Legal-move hints, undo, a live disc count and animated flips make it a friendly place to learn; the board is even fully keyboard-playable with arrow keys and Enter.

Reversi rewards a beautiful counter-intuition: hoovering up discs early usually loses. Discs only count at the very end — through the mid-game what matters is mobility (keeping more options than your opponent) and the corners, which can never be flipped once taken. Learn to keep your disc count low, avoid the X-squares diagonally touching empty corners, and you will start beating the Hard computer.